1. Field of the Invention
The present invention relates generally to a method for forming a diamond impregnated carbide and specifically to a method for forming a cemented tungsten carbide composite containing dispersed diamond crystals formed via the in-situ conversion of dispersed graphite particles.
2. Description of the Prior Art
A variety of composite polycrystalline diamond bodies are known in the prior art for use as wear resistant and cutting elements. For instance, U.S. Pat. No. 3,850,053 describes a technique for making cutting tool blanks by placing a graphite disk in contact with a cemented tungsten carbide cylinder and exposing both simultaneously to diamond forming temperatures and pressures. U.S. Pat. No. 4, 259,090 describes a technique for making a cylindrical mass of polycrystalline diamond by loading a mass of graphite into a cup-shaped container made from tungsten carbide and diamond catalyst material. The loaded assembly is then placed in a high temperature and pressure apparatus where the graphite is converted to diamond.
U.S. Pat. No. 4,525,178 shows a composite material which includes a mixture of individual diamond crystals and pieces of precemented carbide. The mixture is heated and pressurized to create intercrystalline bonds between the diamond crystals and chemical bonds between the diamond crystals and the precemented carbide pieces.
The prior art reveals methods for making diamond impregnated cemented carbide in which diamond particles are blended with carbide powder and either a hot press or high pressure, high temperature apparatus (HPHT) is used for final sintering. However, such techniques have suffered from several disadvantages, the primary disadvantage being less than optimum diamond retention. U.S. Pat. No. 4,525,178 was an attempt to improve upon the prior art. Instead of blending diamond crystals with a tungsten carbide matrix powder and processing the blend using powder metallurgy technology, chunks of sintered tungsten carbide were ground up and mixed with diamond crystals. The mixture of diamond crystals and precemented carbide chunks was placed into a HPHT apparatus to sinter the materials into a solid composite body. The process was dependant upon forming intercrystalline bonds between diamond crystals and precemented carbide particles. The technique was also limited in the shapes that could be formed because low density green bodies were placed in an HPHT apparatus capable of reaching conditions in excess of 40 kilobars pressure and 1200.degree. C. temperature. The shapes which could be formed were limited to those shapes which could be formed in an HPHT press. It was also not possible to make a composite having a diamond grain size which was on the order of magnitude of the size of the individual carbide grains, since the prior art process employed chunks of precemented carbide as a starting material.
A need exists for an improved method for forming a diamond impregnated carbide in which standard powder metallurgy starting materials are utilized.
A need also exists for an improved method for producing a diamond impregnated carbide which does not rely upon the use of diamond crystals and precemented carbide particles as starting materials.
A need also exists for an improved method for forming a diamond impregnated carbide, the carbide being produced in any of the shapes currently possible with standard tungsten carbide powder technology.
A need also exists for a method for forming a diamond impregnated carbide in which skeletal diamond crystals produced in-situ are intergrown and intertwined with the individual carbide grains.
A need also exists for a method for forming a diamond impregnated carbide suitable for use as a wear resistant pad or cutting structure which has improved abrasion resistance and diamond retention characteristics.